In the prior art, combination rotary machines for sheet metal bending have long been in use. They comprise upper and lower shafts on which various kinds of rollers are mounted for many different uses.
Although many thousands of such machines have been in use, yet no way has been found in the prior art to use them for making round starting collars.
A starting collar is a circular protrusion or collar extending from a cylindrical pipe about its circumference and spaced from a terminal end thereof. When that terminal end is inserted through a sheet metal wall, the portion of the inserted duct which protrudes beyond the wall is then bent back against the inner side of the wall to hold the wall securely between bent-back ears of the duct and the collar.
Such walls frequently have insulation on their inner sides so that the tabs must be long enough to grip the inner side of the insulation. As insulation can vary in thickness, it is an object hereof to provide a machine which can make the collar at a gauged selected distance from the end of the cylindrical duct.
In round collar making without the guide roller hereof, the work piece is placed between the main rollers, but as the rollers are rotated the cylindrical workpiece becomes distorted because of the tendency of the metal going between the rollers to continue in a straight line.
This distortion causes it to be difficult to fit the distorted work piece into the circular hole in another piece of metal and much time is consumed in craming them in.
So one objective hereof is to eliminate this waste cramming labor by providing the concept of placing a guide roller in addition to two collar-making rollers on a combination rotary machine for making collars thereon that are truly cylindrical and that will fit into circular holes speedily.
Another objective is to provide for the double use of the two rollers, and of the combination rotary machine, not only for round collar making but also for lock seam opening.